Frequency conversion by 3-wave nonlinear processes is the conversion of electromagnetic radiation from one frequency into two other frequencies or from two into one. Second-harmonic generation is a special case in which two photons of the same frequency are combined into a single photon of twice the frequency. Other 3-wave nonlinear optical processes are difference-frequency generation, sum-frequency generation, optical parametric oscillation, and optical parametric generation. Optical frequency conversion can occur when an intense beam of light passes through a nonlinear optical material, such as KDP or BBO. By properly aligning the beam with respect to the crystal lattice, it is possible to greatly enhance the frequency conversion effect through a phenomenon known as phase matching. This occurs when the interacting light travels through the material with the same velocity and phase, extending the interaction distance and increasing the conversion efficiency.

Gooch and Housego has considerable experience in the design and production of crystals for nonlinear frequency conversion applications from the deep UV to the far IR. A wide selection of materials, including, but not limited to AgGaS₂, AgGaSe₂, BBO, CdS, CdSe, CLBO, KDP, and KD*P are available. Several proprietary software routines enable us to supply "optimized" crystals, which allow you to get the best possible performance from your system. Crystals as large as 41 cm X 41 cm X 1 cm for ICF applications and as small as a few millimeters in cross-section for microchip laser applications are routinely produced. Special geometrical shapes include thin plates, having a 200:1 diameter to thickness ratio with diameters as large as 160 mm and plates as thin as 400µm for femtosecond-pulse-duration applications. Brewster-cut bars are supplied for low-loss intra-cavity laser applications. Our combined capabilities of crystal growth, device design and assembly, optical fabrication, AR coating, and performance testing result in products with superior performance.